Climate Change &
Sea Level Rise

Related information

This unprecedented restoration effort, in the middle of a major urban center, will transform a landscape the size of Manhattan into a thriving wetland ecosystem— providing a critical natural buffer against the effects of global climate change and sea level rise.

The Wetland Sponge Effect: A Long Term Solution to Flooding Around the Bay

The expansive tidal wetlands that once circled the edge of San Francisco Bay served as natural buffers against flood events. Unfortunately, San Francisco Bay has lost more than 85% of its tidal wetlands. Once established, newly restored wetlands act as giant sponges, absorbing floodwaters during storm events and slowly releasing runoff back into the Bay.

Because of historic land subsidence in Silicon Valley, some of California’s most valuable business real estate is at risk of tidal flooding. The Restoration Project will construct a series of levees coupled with tidal marshes on their outboard side. Once established, these outboard tidal marshes will be the first line of flood defense and will help protect the levees from storm wave action and tidal surge.

Restored tidal wetlands also increase the flood carrying capacity of local creeks, flood control channels, and rivers. By scouring the mouths of these waterways and reestablishing their connection to historic flood plains, new tidal marshes will help maintain existing flood control infrastructure.

Tidal Marshes Grow as Sea Levels Rise

Tidal marshes develop by gathering sediments and growing vegetation as sea levels rise. As sediment washes into newly opened salt ponds, it accumulates and begins to establish new tidal plains for marsh vegetation.

The South Bay is an excellent place for sediment deposition and this bodes well for the development of new tidal marsh. Studies have shown that marshes in the South Bay remained intact, even between 1940 and 1960 -- a time when sea level was already rising and the land was subsiding rapidly due to groundwater extraction in Santa Clara County.

Once tidal marshes are established they become very efficient sediment traps. In effect, they tend to preserve themselves as they age, provided that enough sediment is available in the Bay. For this reason new tidal marsh areas are likely to keep pace with changing sea level conditions.

Tidal Marshes Capture Carbon

Because tidal marshes are such biologically productive habitats, they capture significant amounts of carbon from the atmosphere. Unlike many freshwater marshes, tidal saltwater marshes release only negligible amounts of methane, a powerful greenhouse gas. As a result, the carbon storage benefits of tidal salt marshes may exceed those of freshwater marshes. Tidal marshes may be more efficient per unit area than trees when it comes to removing carbon from the atmosphere.

Given enough sediment, tidal marshes continue to grow and pull carbon dioxide out of the atmosphere as sea levels rise. While specific research is needed to quantify the carbon sequestration capacity of the South Bay Salt Pond Restoration Project, there is no doubt that restoring tidal marsh is an effective method for removing carbon dioxide from the atmosphere and helping to reduce the effects of climate change.